Just depends - that's a long way into the future. Only a decade more than the time between the first proper bicycle (1863) and the first satellite (1957).

It all depends of course, on whether we continue with space exploration as we are doing now.  Seems no sign of it slowing down yet anyway, indeed more of a boom.

If so, I could see humans setting foot directly on the Moon, Mercury, Phobos and Deimos, any of the asteroids, Callisto - outermost of the Jovian moons, relatively accessible, and - if we manage closed system spacecraft - no reason why they can't go further afield, even set foot on Pluto. I think at least a couple of decades to sort out all the issues about finding ways for humans to survive for years on end in space without resupply from Earth. But 2100 is well beyond that.

I can see them occupying floating habitats in the Venus upper atmosphere above the clouds. And it would be possible to send a human to the surface of Venus briefly in a refrigerated spacecraft, are ideas for doing it even now. Even to remain there for some time using heat pumps to pump the heat out of their habitat to keep it cool. Whether anyone would bother and want to take that risk I don't know.

I think it is possible also that they are living in free floating Stanford Torus type habitats which then could be situated anywhere in the solar system. Especially in the inner solar system where there is plenty of sunlight.

But if you say 2100 - well I think there's a fair chance we might have fusion power by then and perhaps microfusion plants just meters across. If so then humans would become independent of the sun and could set up habitats anywhere even in the distant Oort cloud comets.

I don't think they would necessarily set foot on Mars by then. Depends what we find there. But if we find native present day Mars life, then for instance Chris McKay has argued we should leave Mars to the Martians even if they are just microbes, and I think there is good reason for that myself also as you'll see from my other answers. Especially if we find life there based on a totally different, non DNA based biochemistry - or for instance, early RNA based life vulnerable to our more recent DNA life or some such. It could be of such interest, easily, that we decide collectively that it has to be protected from Earth life.

But we may well have robots exploring it and humans also exploring it from orbit via telepresence, so good by then surely that it would feel very much as if you are actually there, but with heightened senses.

Same for Europa. By then hopefully we have developed 100% sterilization capabilities for our rovers and telebots and would be able to explore the Europa oceans without any risk of introducing Earth life. If we are very lucky, perhaps we find higher lifeforms there, or even intelligent lifeforms like ourselves (but without technology).

I think there's a decent chance that even by 2050 we have the ability to send a hundred tons or more into orbit around Earth at low cost, perhaps even flying directly into orbit much as we fly to another continent, and be able to get to Mars or Venus in weeks from Earth, instead of months.

We could have sent our first interstellar robotic probes by then also, may even have had a signal back if they are reasonably fast - at a tenth of the speed of light, a probe could get to the nearest star Proxima Centauri in 42.4 years

All of this I think has upsides but also downsides. We would have to be much more peaceful than we are now, to have many people in space, especially if it gets into say the hundreds of thousands because they'd have access to technology more powerful than our present day ICBMs.

And I think by then we may well have found signals from extra terrestrials living around distant stars or other galaxies. If so hopefully they will educate us about some of the hazards to watch out for as we develop further technologically.

I think that if we have easy portable fusion power we'd also have the capability to mount interstellar expeditions, even just by hopping from one comet to another in the Oort cloud until eventually we get to the point where it makes sense to colonize comets that orbit other stars. Not that we'd get there so soon, but that we'd see the possibility of endless outwards expansion.

But if so, then it would be something that requires great care and may be that we decide it is far safer to send robots instead. For details, see Self Replicating Robots - Safer For Galaxy (and Earth) Than Human Colonists - Is This Why ETs Didn't Colonize Earth?

By then also surely we have mapped out every single asteroid of any size in the entire solar system. Probsably right out to Pluto. Leaving no chance at all of an unexpected asteroid impact.

It wouldn't be that hard to do with a small advance in technology. We are already in the situation where without much by way of funding compared to nuclear weapons and spy satellites we could map all the NEOs down to 20 meters or so.

And surely would have stopped climate change by then. Our population would already have leveled off or even be declining world wide, according to the middle of the range predictions. And generally I'm optimistic there.

So we wouldn't be in space because of pressure from an over populated world. And with our knowledge of every single asteroid in the solar system, it would be easy to defend Earth against them even if there was a big 10 km diameter one headed our way in the 22nd century (one in a million chance).

So - either we sort ourselves out, or we don't.  If we do, which I'm optimistic we will do, it could easily be a quite bright future by then. Though only the first steps of a very young civilization. I see no reason why we can't continue as we are as a species, a technological species, for millions of years. Over timescales of tens or hundreds of millions of years, we'd probably evolve to new creatures.

So I have an optimistic view of the future myself :). Hopefully we can reach some future like this. Though what I just described will surely feel hopelessly dated even maybe a couple of decades from now  -that's the almost inevitable case for all future predictions especially involving technology. Still, is fun to speculate.